Abstract
This paper presents a developed isobaric expansion heat engine and preliminary measurements made with the engine operating as a pump, as well as a comparison of the experimental results with a thermodynamic model. Experiments were carried out at heat source temperature in the range 30-90 degrees C and heat sink temperature around 11 degrees C; refrigerant R134a was used as the engine working fluid. The pressure difference generated by the engine-pump varied from 2.5 bar at the heat source temperature of 30 degrees C to 23 bar at the heat source temperature of 86 degrees C. At an engine cycle frequency of about 0.25 Hz, the engine operates with a useful power up to 500 W, and a water pumping flowrate up to 15 L/min. Depending on the temperature of the heat source the obtained efficiency was 3.5-6 %. This efficiency looks very high, considering such a low-temperature difference (20-75 degrees C) and low power (<1 kW). The difference between the experimental and thermodynamic efficiency is <25%, which indicates low mechanical and thermal losses. The results are very promising showing that the engine is a valuable alternative to the current technologies, especially at low temperatures (<100 degrees C) and low power range (<500 kW). The presented technology is easily scalable and reproducible in all industries where there is a temperature difference > 20 degrees C. High pressure pumps for water desalination and heat engines for generating mechanical energy (electricity) using geothermal, biomass and solar energy, waste heat of diesel engines, as well as of SOFCs and LT-PEM fuel cells are examples of promising applications.
NSTL
Elsevier